The invention relates to improvements in centrifuges, and more particularly to a self-discharging centrifuge for the separating of materials of different densities such as solid liquid mixtures wherein the separating vessel discharges the separated heavy materials through an annular gap, the size of which is controlled by a slide valve which moves axially to control the size of the gap, and the improvement resides in the arrangement of the centrifuge and particularly in the slide valve structure and the control therefor.
A form of self-discharging solid jacket centrifuge is shown and described in U.S. Pat. No. 3,823,868. In this structure a separator vessel is provided rotatable about its central axis and an axially movable or sliding circular valve is moved back and forth to control the size of an annular discharge gap which opens from the separating vessel and releases the heavy materials which have been separated. In U.S. Pat. No. 3,823,868, a circular slide valve is urged toward closed position by a spring. To open the gap and increase its size, liquid is introduced into a pressure chamber which is open to the outside. The sliding circular valve is moved against the spring power of the spring element in the opening direction and thereby opens the outlet gap. The pressure chamber of the structure of this patent has nozzle shaped radially extending openings through which the liquid can escape out of the pressure chamber. This arrangement provides disadvantages in that the sliding circular valve can be moved only during operation of the centrifuge against the force of the spring to open the gap. An arrangement may be provided wherein the spring urges the gap toward open position and the pressure chamber closes the gap, but in either arrangement when the separator is at a standstill and is not rotating, the gap is held either in a closed or open position. This results that if the rotation of the separator stops, the centrifuge drum is therefore either unintentionally emptied or remains filled. Further, no function monitoring of the sliding circular valve at standstill of the centrifuge is possible.
Further, in this prior art structure of U.S. Pat. No. 3,823,868, because the pressure chamber is open to atmospheric pressure, and it depends on the slow release of liquid through the radial openings in the wall from the pressure chamber, opening and closing of the outlet gap cannot be accomplished speedily and movements or change in opening is significantly retarded. This has a disadvantageous effect on the discharge of the separated substances out of the centrifuge vessel.
Also, in accordance with this prior structure, the movement cycle in the position of the sliding circular valve and the width of the outlet gap cannot be monitored. The operator will never know precisely when the outlet gap is entirely opened or whether it is closed or when it is closed by the sliding circular valve. The movement of the sliding circular valve and the opening and closing of the outlet gap is dependent not only on the rotation or operating state of the centrifuge but also on the solid liquid mixture which is located in the vessel and the pressure of this liquid which is generated by the centrifugal force, and therefore the opening gap can be controlled only with great difficulty, but cannot be controlled at all when the structure is not rotating.
In German Pat. No. 294,381, a centrifuge structure is disclosed whereby the sliding circular valve which lies outside can be moved in a closing and opening direction with the help of several twin piston cylinder units which are arranged in the floor of the separating vessel. This device for the movement of the sliding circular valve is complicated and expensive.
An object of the invention is to provide a device which makes possible a rapidly operating continuously adjustable valve displacement which is independent of the operating state of the separator.
A further object of the invention is to provide a separator with a controllable discharge valve arrangement which provides advantages and objectives and accomplishes an improved separating function avoiding disadvantages present in the prior art.
A feature of the invention is to provide a control for an annular slide valve for a separator where the control operates by a pressure chamber operative to move the valve in a closing direction and the pressure chamber is supplied with pressurized fluid to align with a control device positioned outside of the centrifuge with the control device controlling the inlet to the pressure chamber and/or the outlet of the fluid from the pressure chamber thereby controlling the closing and opening of the sliding circular valve. The invention further employs a spring means biasing the valve in a direction opposite the action of the pressure chamber.
In accordance with a preferred form of the invention, the sliding circular valve is moved by the pressure medium in the pressure chamber only in the closing direction while movement of the valve in the opening direction is accomplished by a spring biasing means. Because of this arrangement, the movement of the sliding circular valve and thus the opening and closing of the outlet gap, can be accomplished in a short time on the order of less than 0.1 seconds.
Further, in accordance with the preferred arrangement of the invention, the closing force and therefore the contact pressure of the sealing edge of the sliding circular valve can be varied or controlled and optimumly adjusted for each operating state. This makes possible the adjustment of the closing force of the sliding circular valve in such a manner that in the event of a predetermined filling of the separating vessel, the opening pressure due to the material can create a self-acting discharge and overloading of the centrifuge drum is avoided. Further, control can be effected on the discharge valve completely independently of the operating state of the separator, and the annular gap can be adjusted larger or smaller as needed. This makes possible an increase or decrease in the discharge of heavy material which is separated in the centrifuge drum and makes possible an optimum accommodation to the substances, that is, the solid liquid mixtures which are to be separated in the centrifuge and permits accommodating them to engineering requirements of coacting ancillary systems.
In a preferred form of the invention, the pressure chamber is arranged in the central region lying close to the axis of rotation of the separator and located between the floor of the sliding cylindrical valve and the floor of the separating vessel. With this construction, the pressure chamber can be dimensioned relatively small so that is effectiveness is more favorable, and a quick closing and a quick opening of the gap can be accomplished. A pressure chamber of this design has the advantages which are required by an operation where control is essential and makes it capable to move only very small quantities of pressure medium with a resultant attainment of quick movement of the sliding cylindrical valve.
In a further arrangement of the preferred embodiment, the control device includes a pilot valve which is arranged in the fluid pressure supply line, and also includes a volume control element for the pressure medium which is operative in connection with the pilot valve. With the aid of these elements, the movement of the sliding cylindrical valve and hence the opening and closing of the gap from the separation vessel can be carried out in a uniquely simple and economical manner.
The volume control element consists of a double acting piston and cylinder unit with a piston rod on one side which operates cooperatively with an adjustable stop. Using this stop, the width of the outlet orifice which is required or desired in each case can be precisely adjusted.
Further in accordance with the preferred arrangement, in the cylinder wall of the double operating piston and cylinder unit there is arranged an end position scanner or measuring device for the piston rod. With the help of this end position measure or caliper, both the width of the outlet gap can be determined and the opening and closing movement of the sliding valve can be monitored.
Other objects, advantages and features will become more apparent with the further teachings of the principles of the invention in connection with the disclosure of the preferred embodiments described and shown in the specification, claims and drawings, in which: